This invention relates to a rubber composition adapted for use as a material in producing hoses such as refrigerant hose, radiator hose, hot water hose, steam hose and other hoses; a hose having an inner tube and/or an outer cover comprising such rubber composition; and a process for producing a refrigerant hose having an inner tube comprising such rubber composition.
Rubbers such as EPDM and IIR have been used for the rubber components of the rubber composition for refrigerant hose, radiator hose, hot water hose, steam hose and other hoses. More recently, a halogenated copolymer of an isomonoolefin and a p-alkylstyrene (hereinafter referred to as BIMS) have been used since BIMS has been found to satisfy both the moisture impermeability and weatherability (ozone resistance). For example, Japanese PCT Publication A 6-506013 discloses a composition for mold curing elements containing a BIMS, a filler, a process oil, and a curing agent; and Japanese PCT Publication A 8-500385 discloses a rubber composition comprising a BIMS containing at least 5% by weight of a p-alkylstyrene and at least about 0.4% by mole of a halogen, a filler, a rubber additive, and a curing agent.
JP-B 7-116339 discloses that a rubber composition primarily adapted for producing a hose which comprises a BIMS having a particular ratio of the Br content to the p-alkylstyrene content and zinc salt of a fatty acid as a vulcanization aid exhibits good adhesion with fibers. JP-A 9-124848 discloses an elastomer composition containing a BIMS and a thermoplastic resin, and more particularly, a thermoplastic elastomer composition adapted for producing a hose of reduced permeability comprising resin components including a BIMS of a particular p-alkylstyrene content and a particular halogen content and a thermoplastic resin, and wherein at least a part of the resin components constitutes continuous phase and at least a part of the resin components constitutes dispersed phase.
In the use of such a hose, the hose is connected to the particular system by coupling the hose at either end with a metal coupling, and such connection of the hose to the system and prevention of the leakage of the refrigerant or the like at the connection are realized by the resilience of the deformed hose. As a consequence, prevention of the refrigerant leakage at and/or near the metal coupling, the compression set resistance is heavily influenced by the modulus at the temperature of use of the rubber composition constituting the inner tube and/or the outer cover of the hose and compression set by aging. The compression set which greatly affects the leakage for metal coupling of the hose, of the BIMS has been superior to IIR but inferior to EPDM, and improvement in the compression set of the BIMS has been awaited. Compression set has been known to be greatly affected by the vulcanization system of the rubber composition. The vulcanization system of the BIMS is not fully elucidated due to its uniqueness, and for example, a BIMS which has excellent compression set suffered from inferior scorch resistance and insufficient processability (burning). A BIMS which has an improved balance between the compression set and other properties, and in particular, the scorch is not yet known.
A refrigerant hose is also required to have a gas (refrigerant) impermeability (barrier properties for a refrigerant). A barrier resin such as polyamide resin is often used for the innermost layer which is in contact with the refrigerant. A hose is also expected to have an improved vibration absorbability in view of the higher requirements for the comfort and ride of a car.
Some barrier resins with high refrigerant barrier properties has a high Young""s modulus and inferior flexibility, and when such resin is used for an automotive hose, absorbability for the vibration and noise from compressors is insufficient to contribute for the prevention of the vibration and noise transmission. No material and no technology have so far been developed that have realized both the gas impermeability and the vibration absorbability at a sufficient level.
The present invention has been completed in view of the situation as described above, and an object of the present invention is to provide a rubber composition adapted for producing a hose which has excellent scorch property and compression set, and which can be stably worked into a hose having sufficient moisture impermeability, ozone resistance, and compression set; a hose produced by using such a rubber composition set; as well as a rubber composition adapted for use in producing a hose having excellent gas impermeability and vibration absorbability; and a refrigerant hose and method for producing the same.
In order to obviate such problems, the inventors of the present invention have carried out an intensive investigation and found out that, by using of a rubber composition comprising a combination of a BIMS of particular compositional range and a particular vulcanization system, a hose can be produced without suffering from scorch and adhesion between the hose inner tube and the exterior reinforcing layer is increased, and as a consequence, burst pressure, compression set resistance, moisture impermeability and ozone resistance are improved. The inventors also found that a refrigerant hose having excellent gas impermeability and vibration absorbability in addition to the above-mentioned properties can be produced by extruding the inner tube of the hose in an extruder of particular structure using a rubber composition comprising a BIMS of particular compositional range blended with a particular filler. The present invention is completed on the bases of such findings.
According to first aspect of the present invention, there is provided a rubber composition for hose production comprising
(A) 100 parts by weight of a brominated copolymer of a C4-7 isomonoolefin and a p-alkylstyrene (PMS) wherein p-alkylstyrene content is 5 to 25% by weight and bromine (Br) content is at least 1.5% by weight, and weight ratio of bromine unit to p-alkylstyrene unit is such that 0.15 less than Br/PMS less than 0.40;
(B) 0.1 to 10 parts by weight of zinc white; and
(C) 1 to 15 parts by weight of brominated alkylphenol resin, and
a hose produced by using such rubber composition for the inner tube and/or the outer cover.
According to second aspect of the present invention, there is provided a rubber composition for hose production comprising
(A) 100 parts by weight of a brominated copolymer of a C4-7 isomonoolefin and a p-alkylstyrene (PMS) wherein p-alkylstyrene content is 5 to 25% by weight and bromine (Br) content is at least 1.5% by weight, and weight ratio of bromine unit to p-alkylstyrene unit is such that 0.15 less than Br/PMS less than 0.40; and
(D) 25 to 200 parts by weight of an inorganic laminar compound or 20 to 200 parts by weight of talc, and,
a hose produced by using such rubber composition for the inner tube.
According to third aspect of the present invention, there is provided a rubber composition for hose production comprising
(A) 100 parts by weight of a brominated copolymer of a C4-7 isomonoolefin and a p-alkylstyrene (PMS) wherein p-alkylstyrene content is 5 to 25% by weight and bromine (Br) content is at least 1.5% by weight, and weight ratio of bromine unit to p-alkylstyrene unit is such that 0.15 less than Br/PMS less than 0.40;
(B) 0.1 to 10 parts by weight of zinc white;
(C) 1 to 15 parts by weight of brominated alkylphenol resin; and
(D) 25 to 200 parts by weight of an inorganic laminar compound or 20 to 200 parts by weight of talc, and
a hose produced by using such rubber composition for the inner tube.
According to fourth aspect of the present invention, there is provided a rubber composition for hose production comprising a process for producing a refrigerant hose comprising at least two layers of an inner tube and a reinforcing layer on the exterior of the inner tube, wherein said inner tube is fabricated from the rubber composition according to said second or third aspect of the invention, and said inner tube is formed by in-die drawing method wherein drawing ratio (a/b) of the cross-sectional area at the die inlet (a) to the cross-sectional area of the extrudate at the die outlet (b) is at least 5.